option to turn off acpiirq

Reference: /n/atom/patch/applied/acpiirqoff
Date: Mon May  5 21:44:08 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/devacpi.c	Mon May  5 21:44:08 2014
+++ /sys/src/nix/k10/devacpi.c	Mon May  5 21:44:08 2014
@@ -354,6 +354,7 @@
 static void
 init(void)
 {
+	char *p;
 	int i;
 
 	aconf.powerbutton = acpipoweroff;
@@ -371,6 +372,9 @@
 
 	initgpes();
 
+	p = getconf("*acpiirq");
+	if(p != nil && atoi(p) == 0)
+		return;
 	/*
 	 * This starts ACPI, which requires we handle
 	 * power mgmt events ourselves.